Titanium and its alloys have been utilized as desirable materials for dental and orthopedic prostheses because of their excellent corrosion resistance, biocompatibility, mechanical properties, and high strength-to-weight ratio. [1-4] However, one major concern regarding the use of these titanium prostheses in medical or dental applications is the mismatch of the Young's modulus between the bone (10-30 GPa) and the titanium material (110 GPa). [5,6] Because of that mismatch, bone is often insufficiently loaded and becomes stress-shielded, which then leads to higher bone resorption. Indeed, this mismatch of the Young's moduli has been identified as a factor for the loosening of dental implants that occurs following stress shielding of bone and may result in detrimental resorptive bone remodeling. [7-8]
Recently, the introduction of an amount of porosity into titanium and its alloys, both of which are typically used to produce at least a portion of current dental prostheses, has been proposed to reduce the Young's modulus of titanium and potentially overcome the foregoing detrimental effects. [9] To date, however, the introduction of a sufficient degree of porosity into titanium-based prostheses has yet to be completely achieved, both from a customization standpoint and from an economical standpoint. Modern dental prostheses, such as dental implants, are predominantly produced by the machining of solid titanium rods, followed by applying different surface treatments and geometries to improve stability and enhance osseointegration of the prostheses. However, none of the conventional techniques are capable of producing a controlled porosity, much less a completely controlled geometry and external surface morphology in a limited number of steps. [10-13]
Researchers have also proposed the placement of custom-made root-analogue implants into an extraction socket to reduce bone and soft-tissue trauma. [24] In those initial clinical studies, root-identical titanium implants demonstrated favorable results with 100% primary stability at insertion and 1-month follow up; however, an extremely high failure rate of 48% was then found over a short time period of 9-months post-operation. [25-27] In a more recent clinical trial, immediate, non-submerged, custom-made root-analogue zirconia implants (with surface macro-retentive feature and reduced implant diameter at the cortical bone area) placed into single-rooted extraction sockets showed an overall survival rate of 92% as late as 33 months under functions. [28] Satisfactory esthetic and functional results were also achieved with the composite crowns in those studies, with minimal soft and hard peri-implant tissue resorption being observed, but the ability to produce custom-made prostheses with a user-defined complexity was nonetheless still limited.
Similar to the issues encounter in fabricating implants, ceramic materials have been used for decades to improve esthetic outcomes (i.e., the appearance) of dental restorations. In fabricating such dental restorations, the intent has been to closely imitate the optical properties of natural teeth, while maintaining acceptable biomechanical characteristics and biocompatibility. With the several ceramic materials (glass and oxide ceramics) and methods for fabrication (conventional, press and Cad-Cam) that are currently employed, however, each of the currently-available ceramic dental restorations exhibit a number of shortcomings, including a higher incidence of fracture compared to prostheses fabricated exclusively out of dental alloys.
Accordingly, a method of fabricating a dental prosthesis, such as a dental implant or dental restoration, that allows greater control over the mechanical properties of the dental prosthesis, but that is also capable of producing a custom-made prosthesis having a desired physical geometry and external surface morphology in an efficient and economical manner would be both highly-desirable and beneficial.